Question: Why is Blasting necessary?
Answer: In any kind of construction, quarrying or mining
operation, blasting is generally considered the quickest and least
costly method of removing rock. If explosives could not be used,
many projects would become unreasonably expensive and would simply
not be built. Blasting makes it possible for all of us to have
new highways, transportation systems, and improved utilities.
It allows for residential development to provide housing and
commercial development to provide jobs. And blasting results
in more affordable consumer prices for coal and other products
that come from rocks and minerals.
Question: How close can they blast to my house?
Answer: In all surface mining operations, no blasting
shall be done within 300 feet of any home unless approved in writing
by the property owner. There are no distance limitations governing
construction blasting. However, airblast and ground vibration
limits may not exceed state standards regardless of distance from
the blast.
Question: If dishes rattle, is my house being damaged?
Answer: Homeowners should not be surprised that even when
blast vibration levels are far below the legal limit, highly perceptible
vibration can be experienced inside the home; windows and dishes
might rattle, knickknacks and pictures might move or fall if not
securely fastened, and swag lamps or chandeliers might sway.
These effects can be generated by ground vibration or airblast
acting separately or together, and can last from one to three
seconds or more depending upon the distance from the blast, geologic
influences and other factors. Despite these sometimes startling
effects, there is absolutely no correlation between how a blast
"feels" and its potential for causing structural damage
to a home. In fact, cultural stresses (e.g., doors slamming,
kids jumping, people ascending or descending stairs) and natural
stresses (e.g., sunlight, wind, rain, temperature and humidity
fluctuations and changes in soil moisture) place greater stresses
on a home than legal blast vibrations.
Question: How will blasting effect my water well?
Answer: Blastholes are normally drilled vertically and
arranged in a grid pattern. Typical blasthole diameters range
from two to seven inches in quarries and five to nine inches in
surface coal mines, with typical depths from 10 to 70 feet. Upon
detonation, fracturing of rock generally occurs not greater than
20 to 30 feet from any blasthole, depending largely upon hole
diameter and the densities of the rock and explosive. A common
misconception is that fracturing extends far beyond the mine property
- even miles from the blast site. If this were true, the blastholes
could be placed much farther apart than the commonly used spacing
of six to 18 feet in quarries and 12 to 25 feet in surface coal
mines, and blasting would be much more economical since less drilling
and explosives would be necessary.
Question: What is a pre-blast survey?
Answer: A pre-blast survey will document the conditions
of the structure, and record any pre-blasting damage and other
physical factors that could reasonably be affected by blasting
on the proposed permit. A sample of the dwellings water supply
shall be taken to account the quality and quantity of the supply.
Copies of the completed survey will be supplied to the resident
or owner of the structure, the Bureau of Mining and Reclamation
and the operator conducting the survey. Pre-blast surveys are
conducted by an independent company at the expense of the operator.
Question: What are my rights concerning pre-blast surveys?
Answer: The Department requires before any blasting is
approved:
1. All bituminous surface coal operators to notify
all
residents within 1/2 mile of blasting site,
of
their rights to obtain a pre-blast survey.
2. All industrial mineral operators (quarries)
must
seismograph all shots and design for .5 in/sec.
or
less or notify all residents within 1000 feet
of
the blasting site of their rights to obtain
pre-blast surveys.
3. Anthracite surface coal mines and construction
site
operators are not required to offer pre-blast
surveys unless specified by permit condition
or
contract requirements.
Question: What causes ground vibration and how is it measured?
Answer: When a blast is detonated, some the explosive
energy not utilized in breaking rock travels through the ground
in all directions as wave motion, similar to the ripple created
in a pond when a stone hits the water. This wave motion, or ground
vibration as it is commonly called, travels mainly along the surface
at speeds of 5,000 to 20,000 feet per second, depending upon the
density and thickness of the rock and the soil. Its energy level
decreases rapidly with distance from the blast and normally decays
to levels undetectable by humans beyond a few thousand feet.
Because explosives are expensive and vibration represents wasted
energy, it is to the blaster's advantage to utilize as much of
the energy as possible in fragmentation, thereby minimizing vibration.
Blasting seismographs are used to measure ground vibration in
terms of particle velocity, which is the speed at which each particle
in the ground oscillates as the wave motion passes. This would
be similar to measuring the speed of a fishing bobber in a pond
as it moves up and down when a ripple passes under it. Particle
velocity is measured in inches per second, but beyond a few hundred
feet from a blast the actual movement of the ground, or displacement,
is generally only a tiny fraction of an inch, about the thickness
of a piece of paper, or less. So it is important to understand
that a particle velocity reading expressed in inches per second
refers to the speed at which the ground moved, and not
the amount of movement.
Blasters control ground vibration mainly by limiting the weight of explosives detonated within any eight-millisecond period of time. They do this by using millisecond delay detonators (blasting caps) to separate the firing time of each hole from adjacent holes. In a typical 50=hole blast, the result would be 50 smaller and separate explosions instead of one large blast. A common misconception is that the number of blastholes determines the resulting intensity of vibration. However, given the same charge-weight per delay (pounds of explosive detonated within an eight-millisecond period) and the same distance, a 100-hole blast can be designed to produce not more vibration than a 10-hole blast.
Question: What is airblast and how is it measured?
Answer: When a blast is detonated, some energy is lost
to the atmosphere in the form of noise and/or concession. This
phenomenon is caused by the venting of gases through cracks and
fissures and the upward and outward movement of the rock on top
and in front of the blastholes. The resulting increase in the
air pressure is commonly called airblast. Like ground vibration,
airblast levels decrease rapidly with the distance from the blast.
However, airblast travels only at the speed of sound, around
1,100 feet per second, depending upon air temperature, and can
be greater influenced by wind direction and speed, and by atmospheric
temperature inversions which can bend it back toward the earth
and focus its energy several miles away.
Airblast is usually measured with a special microphone connected
to the same type of seismograph that measures ground vibration.
The most common units of airblast measurement are pounds per
square inch (psi) and the decibel (dB), which is based on a logarithmic
sound-pressure scale related to human hearing. The threshold
of hearing begins at zero decibels. An increase of six decibels
represents a doubling of air pressure. As an example, an airblast
measured at 126 dB would have twice the air pressure of an airblast
at 120 dB.
Airblast is controlled mainly by the proper use of stemming material
(the drill cuttings or crushed stones that are shoveled back into
the blasthole after the explosive material has been loaded to
a predetermined depth from the surface) and by not loading explosives
into portions of holes with cracks, voids or mud seams. These
techniques minimize the escape of gases and confine the explosive
energy where it is needed to efficiently break rock.
Question: What are the ground vibration and airblast limits?
Answer: The United State Bureau of Mines (USBM) has conducted
extensive research during the last three decades on the effects
of blast-induced ground vibration and airblast on residential
structures. This research produced recommended limits that, if
adhered to, will effectively protect residential structures from
damage, even if the blasting is repeated on a daily basis over
a period of many years.
Pennsylvania's current regulated limits are:
PPY
AIRBLAST
BITUMINOUS COAL MINE 1.0 133 dB
ANTHRACITE 2.0 133 dB
INDUSTRIAL MINERALS (QUARRIES) 2.0 133 dB
CONSTRUCTION 2.0 NONE
DAMAGE CLAIMS
The Department of Environmental Protection staff will investigate blasting complaints from the public. Blast reports and seismic data are reviewed for completeness, accuracy, and regulatory compliance. The Department has no authority to require compensation if damage occurs. Compensation for damage is strictly a civil matter between the operator and the landowner. Where a potential for damage may exist, the Department may require modification of the blast plan to reduce vibration levels. If the blast plan has been violated, enforcement action will be taken.
SUMMARY:
Contact your local DEP District Mining and Reclamation office with any questions or concerns you may have about blasting.
Pottsville District Office 717/621-3118
COUNTIES: ADAMS, BERKS, BUCKS, CARBON, CHESTER, COLUMBIA, DAUPHIN,
CUMBERLAND, DELAWARE, FRANKLIN, JUNIATA, MONROE, LEBANON, LEHIGH,
LUZERNE, MIFFLIN, MONTGOMERY, PIKE, MONTOUR, NORTHHAMPTON, PERRY,
NORTHUMBERLAND, PHILADELPHIA, SCHUYLKILL, SNYDER, SUSQUEHANNA,
UNION, WAYNE, WYOMING AND YORK.
Hawk Run District Office 814/342-0410
COUNTIES: BRADFORD, CAMERON, CENTRE, CLEARFIELD, CLINTON, POTTER,
LYCOMING, SULLIVAN AND TIOGA.
Greensburg District Office 412-925-5500
COUNTIES: ALLEGHENY, ARMSTRONG, BEAVER, FAYETTE, GREENE, WASHINGTON
AND WESTMORELAND.
Ebensburg District Office 814/472-1900
COUNTIES: BEDFORD, BLAIR, CAMBRIA, FULTON, HUNTINGDON, INDIANA
AND SOMERSET.
McMurray District Office 412/941-7100
ALL COUNTIES WERE MINING AND SUBSIDENCE OCCUR
Knox District Office 814/797-1191
COUNTIES: BUTLER, CLARION, CRAWFORD, ELK, ERIE, FOREST WARREN,
JEFFERSON, LAWRENCE, MCKEAN, MERCER AND VENANGO